The invention disclosed herein relates generally to fastening methods and apparatus and more particularly to a method and structure for securing plastic parts together. The invention has been specifically adapted to assemble electrical switch cases.
Materials commonly referred to as plastics have been known and used for a considerable period of time in the manufacture and fabrication of structural devices and forms. Such materials are being increasingly widely used as new material compositions and forming and fabrication techniques become available. Factors which have contributed to the expansive use of plastics include the relatively low cost of plastic raw materials, and the facts that plastics are easily molded or otherwise formed, and that molding techniques are well developed for producing a vast range of configurations and sizes.
Since many applications of plastics require the securing of two or more parts together, a variety of fastening techniques and apparatus usable with plastic parts have been devised. These include conventional bolts, screws, rivets and adhesives. They also include more specialized methods such as hot swaging and ultrasonic welding. Nevertheless, there is a continued need for improved fastening apparatus and techniques in order to realize the potential advantages of plastics as structural materials.
An ideal fastening technique should have the following features: (1) The fastening means should be integrally formed with the parts to be assembled so as not to require separate fasteners or fastening substances. (2) The fastening process should not be accompanied by wasting of material or creation of waste or scrap. (3) The fastening process should not require more than simple well known tooling. (4) The fastening process should not require the use of heat. (5) The fastening process should require minimum time. (6) The fastening process should result in secure assembly of the parts.
The use of bolts, screws, rivets or adhesives undesirably involves the use of separate fasteners or fastening substances. The use of such fasteners and/or substances is further disadvantageous in that installation adds time to the assembly process. Hot swaging requires the use of heat. It is also a relatively slow process in that heat is required to be applied for a sufficient time to soften the plastic material. Ultrasonic welding basically involves the application of heat to fuse surfaces together, the heat being generated by the application of ultrasonic energy. It is also known that techniques such as ultrasonic welding, bonding and use of adhesives are not adequately effective on some plastic compositions.
The applicant has devised a novel, simple structure and process for quickly assembling plastic parts which does not require separate fasteners or fastening agents or complicated tooling, does not involve material waste, and produces very secure attachment. The process is applicable to parts fabricated of formable or ductile materials in accordance with the general definition of plastic. For purposes of the remainder of this description, plastic is intended to mean ductile or capable of being molded or formed.